The present invention is related to a method for reducing the effect of disturbances, affecting the combustion of a fan burner system, and to a fan burner arrangement with a fan burner. It relates more particularly to a method and an arrangement for measuring the relative change of density of a gas as a function of its pressure and of its temperature, and/or measuring a relative mass flow change of said gas as said function, at an at least nearly constant volume flow of said gas.
In fan burners it is known to act on the mass flow of combustion air and on the mass flow of fuel, e.g. with the aid of a compound open loop feed forward control or with the aid of a compound negative feedback closed loop control according to a desired loading. To ensure an at least nearly optimal combustion at all loading levels, and especially combustion that is substantially independent from influences caused by disturbances, it is known to measure the oxygen content of the flue-gas as a controlled variable and to provide a negative feedback loop control circuit which regulates said oxygen content within the flue-gas to follow or to be kept at a control value, by adjusting the combustion air and/or the fuel fed to the burner. Thereby said oxygen content is clearly not a disturbing variable, as a disturbing variable may, per definitionem, not be changed by the process disturbed thereby. The expenditures for such negative feedback control techniques are relatively high, especially because of the oxygen, sensor to be provided and because of the negative feedback controllers.
Further, problems of stability may here occur and must be resolved which is not always easily done, especially due to the controlled system formed by the combustion chamber and the flue-gas pipes up to the area where the oxygen content measurement is performed which controlled system is a difficult system from the point of view of negative feedback control.
Such problems of stability may in fact be resolved, but with great technical efforts. Such measures to optimize combustion by negative feedback control techniques are disclosed in the EP-A-0 086 337.
For smaller burner arrangements, as for household burner arrangements, the effort required for installing and operating such negative feedback controls is often much too high. On the other hand, the totality of such smaller burner arrangements does significantly contribute to pollution of the air.